State toxicologist Fiona Couper recently stated that violations for driving under the influence of marijuana have not gone up since the passage of Initiative-502. But marijuana legalization is still in its early stages and to be charged with a DUI the driver has to get caught with 5 nanograms per milliliter of active THC in their bloodstream. David Hyde talks with Dr. Marilyn Huestis from the National Institute on Drug Abuse, and tries to make sense of the science of marijuana intoxication.